Flaxseed
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Flaxseed Overview

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Flaxseeds are the hard, tiny seeds of Linum usitatissimum, the flax plant, which has been widely used for thousands of years as a source of food and clothing. There are at least three flaxseed components with potential health benefits. The first is fiber, valuable in treating constipation . Flaxseed also contains alpha-linolenic acid, a type of omega-3 fatty acid similar to the omega-3 fatty acids found in fish oil, but significantly different in other ways, and perhaps offering some of the same benefits. Finally, substances called lignans in flaxseed have phytoestrogenic properties making them somewhat similar to the isoflavones in soy.

The oil made from flaxseed has no appreciable amounts of lignans, but it does contain alpha-linolenic acid. See the articles on Flaxseed Oil and Lignans for more information on these substances.

What Is the Scientific Evidence for Flaxseed?

Constipation

In a double-blind study, 55 people with chronic constipation caused by irritable bowel syndrome received either ground flaxseed or psyllium seed (a well-known treatment for constipation) daily for 3 months. 1 Those taking flaxseed had significantly fewer problems with constipation, abdominal pain, and bloating than those taking psyllium. The flaxseed group had even further improvements in constipation and bloating while continuing their treatment in the 3 months after the double-blind part of the study ended. The researcher concluded that flaxseed relieved constipation more effectively than psyllium.

Cholesterol and Atherosclerosis

Some but not all human studies have found that flaxseed improves cholesterol profile . 2 However, the benefits, if they do exist, are very modest. For example, in a double-blind study of about 200 postmenopausal women, use of flaxseed at a dose of 40 g daily produced measurable improvements in cholesterol profile, but the improvements were so small that the researchers considered them "clinically insignificant." 3 It has been claimed that flaxseed might also have a direct effect in helping to prevent atherosclerosis based on its lignan ingredients, but the evidence upon which these claims are based is limited to studies in rabbits. 4

Cancer

Some evidence hints that flaxseed or its lignan components might have cancer-preventive properties. Observational studies and other forms of highly preliminary evidence suggest that people who eat more lignan-containing foods have a lower incidence of breast and perhaps colon cancer. 5 The lignans in flaxseed are phytoestrogens , plant chemicals mimicking the effects of estrogen in the body: Phytoestrogens hook onto the same spots on cells where estrogen attaches. If there is little estrogen in the body, for example after menopause, lignans may act like weak estrogen. However, when natural estrogen is abundant, lignans may reduce the hormone's effects by displacing it from cells; displacing estrogen in this manner might help prevent those cancers that depend on estrogen, such as breast cancer, from starting and developing. (This is also, in part, how soy is believed to work in breast cancer prevention, although the phytoestrogens in soy are isoflavones .)

Some preliminary research indicates that these lignans may also fight cancer in other ways, perhaps by acting as antioxidants . 6 7

Animal studies using flaxseed and its lignans offer supporting evidence for a potential cancer-preventive or even cancer-treatment effect; several found that one or the other inhibited breast and colon cancer in animals 8 9 and reduced metastases from melanoma (a type of skin cancer) in mice. 10 Test tube studies have found that flaxseed or one of its lignans inhibited the growth of human breast cancer cells, 11 and that the lignans enterolactone and enterodiol inhibited the growth of human colon tumor cells. 12 This preliminary research is promising, but much more is needed before we can draw any conclusions.

Although much of this anticancer work has focused on the lignans in flaxseed, one study also found that flaxseed oil—which contains no appreciable amounts of lignans—slowed the growth of malignant breast tumors in rats. 13

Therapeutic Dosages

According to the European Scientific Cooperative on Phytotherapy (ESCOP), the usual dose of flaxseed for constipation is 5 g of whole, cracked, or freshly crushed seeds soaked in water and taken with a glassful of liquid 3 times a day. 14 Expect effects to begin 18 to 24 hours later. Because of this time delay, it's recommended to take flaxseed for a minimum of 2 to 3 days. Children aged 6 to 12 should be given half the adult dose, while children younger than 6 should be treated only under the guidance of a physician. 15 In one study, people received 6 to 24 g per day of flaxseed for 6 months for constipation caused by irritable bowel syndrome. 16 To soothe an upset stomach, soak 5 to 10 g of whole flaxseed in a half cup of water, strain after 20 to 30 minutes, then drink. 17 For painful skin inflammations, the recommended dose is 30 to 50 g of crushed or powdered seed applied externally as a warm poultice or compress. 18 Like other sources of fiber, flaxseed should be taken with plenty of fluids, or it may actually worsen constipation. Also, it's best to start with smaller doses and then increase.

References

  1. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
  2. Arjmandi BH, Khan DA, Juma S, et al. Whole flaxseed consumption lowers serum LDL-cholesterol and lipoprotein(a) concentrations in postmenopausal women. Nutr Res. 1998;18:1203-1214.
  3. Dodin S, Lemay A, Jacques H, Légaré F, Forest JC, Mâsse B. The effects of flaxseed dietary supplement on lipid profile, bone mineral density, and symptoms in menopausal women: a randomized, double-blind, wheat germ placebo-controlled clinical trial. J Clin Endocrinol Metab. 90(3):1390-7.
  4. Prasad K. Dietary flax seed in prevention of hypercholesterolemic atherosclerosis. Atherosclerosis. 132(1):69-76.
  5. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 29(2):95-120.
  6. Sung MK, Lautens M, Thompson LU. Mammalian lignans inhibit the growth of estrogen-independent human colon tumor cells. Anticancer Res. 18(3A):1405-8.
  7. Prasad K. Hydroxyl radical-scavenging property of secoisolariciresinol diglucoside (SDG) isolated from flax-seed. Mol Cell Biochem. 168(1-2):117-23.
  8. Thompson LU. Experimental studies on lignans and cancer. Baillieres Clin Endocrinol Metab. 12(4):691-705.
  9. Thompson LU, Rickard SE, Orcheson LJ, Seidl MM. Flaxseed and its lignan and oil components reduce mammary tumor growth at a late stage of carcinogenesis. Carcinogenesis. 17(6):1373-6.
  10. Yan L, Yee JA, Li D, et al. Dietary flaxseed supplementation and experimental metastasis of melanoma cells in mice. Cancer Lett. 1998;124:181-186.
  11. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 29(2):95-120.
  12. Sung MK, Lautens M, Thompson LU. Mammalian lignans inhibit the growth of estrogen-independent human colon tumor cells. Anticancer Res. 18(3A):1405-8.
  13. Thompson LU, Rickard SE, Orcheson LJ, Seidl MM. Flaxseed and its lignan and oil components reduce mammary tumor growth at a late stage of carcinogenesis. Carcinogenesis. 17(6):1373-6.
  14. Fascicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany: IDW-Verlag. 1997:1-5.
  15. Fascicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany: IDW-Verlag. 1997:1-5.
  16. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
  17. Fascicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany: IDW-Verlag. 1997:1-5.
  18. Fascicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany: IDW-Verlag. 1997:1-5.
 
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